This invention relates to a marine stern drive oil cooling and circulating as well as pumping system. Such stern drives are contemplated for use with a marine internal combustion engine which is mounted inboard of a boat. The rotary engine output is connected through the boat transom to the stern drive unit, which is mounted to the transom and which includes suitable upper and lower gear cases. A vertical drive shaft is suitably mounted within the lower gear case. The drive shaft is rotatably driven by the engine output shaft, and in turn rotatably drives a lower horizontal propeller shaft. The various shafts are mounted on suitable bearings. In addition, stern drive units have included a water passage in the drive housing for receiving engine cooling water through submerged intake ports and transferring the water upwardly and ultimately to the engine.
It is desired that the moving parts of the stern drive unit be suitably lubricated. Prior known lubricating systems have included a series of oil containing interconnected passages and chambers extending from top to bottom of the stern drive unit and which are in communication with the various shafts and bearings. The oil passages and chambers have been arranged remote from the cooling water passage and provide a recirculating path for the oil. Some prior marine propulsion devices have included pumping devices associated with the vertical drive shaft for circulating the oil. These known pumping devices have included internal helixes on the interior of the drive shaft's fixed guide sleeve, such as is suggested in U.S. Pat. No. 4,650,430. Interior threads have also been used on the sleeve. The drive shaft bodies in these instances have been plain and uninterrupted. Other known devices have included a screw formation on the drive shaft itself, used in conjunction with a plain uninterrupted interior sleeve wall.
The temperature of the oil within the stern drive unit should preferably be as low as possible for maximum effective operation of the lubricating system, and the present invention is primarily directed to a concept which accomplishes this aim. Improved pumping is also contemplated.
In accordance with the various aspects of the invention, oil is circulated upwardly from the propeller housing and through the drive shaft sleeve to the upper gear case. A return oil line is provided and which connects from the upper gear case and downwardly through the lower gear case to the propeller housing. The return line is disposed within the stern drive housing's cooling water passage to create an intercooling or heat exchanging effect whereby the incoming water from a lake or other body of water cools the recirculating stern drive unit lubricant. A combination of threaded drive shaft and internally grooved sleeve is utilized to pump the oil through the system.